In the fields of oceanography and hydrology, a vertical water column may be profiled by lowering a probe through it to measure various characteristics as a function of depth. For example, Seo (U.S. Pat. No. 5,965,994) discloses a winch apparatus attached to a floating platform for lowering a probe through a water column for profiling its temperature, conductivity, etc. Alternatively, probes may be employed for measuring sound velocity, fluorescence, dissolved oxygen, and turbidity. The winch lowers the probe through the water column by unspooling line to which the probe is attached. Alternatively, Archibald (U.S. Pat. No. 4,974,536) discloses a winch apparatus attached to a floating vessel for profiling a water column. Dessureault (U.S. Pat. No. 5,570,303) discloses an automated system for profiling a series of vertical water columns from a moving vessel. While the vessel is underway, the automated system employs a winch affixed to the vessel for alternately lowering and raising the probe through a series of consecutive water columns.
If the probe includes a depth gauge and if the support line includes a data cable, the probe can communicate depth data back to a control mechanism on the vessel for controlling the descent of the probe. When the probe approaches a depth known to be close to the water bottom, it can transmit an instruction to the controller onboard the vessel to reverse the descent process, so as to prevent a collision between the probe and the water bottom. Alternatively, if the probe is being employed in a body of water of unknown depth, the probe can employ a sonar device for sensing its proximity to the bottom. Unfortunately, the inclusion of a data cable contributes significantly to the weight of the support line and, consequently, to the size and power requirements of the winch.
In applications wherein collision between the probe and the water bottom is unlikely, e.g., blue water oceanographic applications, underway profiling is possible using a low power winch if the data line is eliminated and a light weight, high strength line is employed. Rudnick et al disclose a profiling system wherein the probe includes a spool of line that unspools as the probe descends into the water column, in a free fail. (Rudnick, D. et al, J. Atmospheric and Oceanic Technology (2007), vol. 24, pp 1910-1923, “The Underway Conductivity-Temperature-Depth Instrument.”) After the unspooling process is complete, the winch rewinds the line and draws the probe back to the underway vessel. After the probe is recovered, the process may be repeated for serial profiling. Unfortunately, because this system lacks a communication cable, it is not employable in applications where there is a risk of collision between the probe and the water bottom. Also, in order not to interfere with the free-fall descent of the probe within the water column, the winch rapidly unspools the line into the water during the descent phase. Rapid unspooling can occasionally cause line tangling. This occasional line tangling necessitates that the process be monitored and compromises the reliability of the process.
Winches can also be employed to control line tension in various applications wherein the line is deployed horizontally. For example, when towing a probe with a tow line, it is important to avoid exceeding the break strength of the tow line. Bailey (US Pat. App. No. 2012/0160143) discloses a vessel for towing a probe. The probe is attached to a tow line, which is attached a winch, which is incorporated into a tow arm. A control system regulates the torque applied to the winch so as to maintain the line tension in the tow line below its break strength.
In another application, Lindgren (U.S. Pat. No. 4,920,680) discloses a winch for horizontally deploying line from a moving vessel for supporting fish nets. The line unspools from a winch as the vessel moves forward. A control system controls the torque applied by the winch so as to maintain a line tension within an allowable range so as to avoid line breakage.
Controlling line tension can also be important within industrial applications. For example, in the textile field, Morton (U.S. Pat. No. 5,277,373) discloses an apparatus for winding yarn onto a spool using a dancer arm for maintaining a constant line tension so as to prevent yarn breakage. Conversely, Groff (U.S. Pat. No. 8,205,819) discloses an apparatus for unwinding material from a spool while maintaining constant tension. Groff's apparatus feeds material into a processor. The processor draws the material from the apparatus, but requires that the material be maintained within a specified tension range as it is being drawn. As the material is drawn, it unspools from a spool, but a brake, engaged with the spool, applies a constant resistive torque so as to create the tension in the material. As the material unspools, it passes through a tension meter which measures the amount of tension. The tension meter then activates a winch motor, rotationally coupled to the spool, which increases or decreases the resistive torque applied thereto, so as to maintain the tension in the material within the required tension range as it unspools.
What was needed was an apparatus for profiling water columns in shallow water from an underway vessel without the benefit of a data line for avoiding collision between the probe and the water bottom. What was needed was an apparatus capable of rapidly unspooling line from an underway vessel of unknown velocity and in variable weather conditions so as to enable a free-fall descent by the probe within a water column, with no risk of line tangling. What was needed was an apparatus capable of achieving a profile depth accuracy of 10% or better without the use of depth data communicated along a communication cable and without having any a priori information about the transit speed of the ship. This is complicated by the fact that, for a given target depth, the length of line paid out will vary with ship speed and other factors. What was needed was a way to regularize the descent behavior of the probe such that its descent rate becomes independent of ship speed, to a first approximation. What was needed was a reliable way to parameterize the achieved depth in terms of deployment time.